1. Field
The device for pump-off control pertains to control systems for pumping units generally referred to as sucker rod pumps. More particularly the pump-off control interrupter for the pump jack that interrupts the production cycle for a pre-determined time.
2. State of the Art
In the production of oil from the sub-service reservoir, frequently beam type pumping units are common artificial lift devices for producing oil. These, so called, sucker rod pumps reciprocate a down-hole pump mechanism that lifts oil on each upward stroke of the sucker rods and on the down stroke, oil flows into the pump and the process is repeated. Often in producing fluid by artificial means with sucker rod pumps, the oil flowing reservoir surrounding the well does not flow to the pump as fast as the pump can lift the oil and when this happens, the fluid level in the reservoir falls below the top of the pump plunger. A limited amount of oil, if any, flows into the barrel of the pump. At this point, the amount of oil being pumped is decreased and on the down stroke the pump plunger impacts the fluid with a hammer type pounding effect joining the sucker rods. Over long periods of time, this pounding causes fatigue and failure of the sucker rod pumping mechanism.
Various techniques have been developed to control the operation of the sucker rod pumps to minimize the fluid pound effect by disrupting the pumping operation for a sufficient period of time to permit oil from the reservoir to again increase the volume surrounding the well bore so that the plunger of the pump is below the fluid level and permits fluid pumping again.
U.S. Pat. No. 5,823,262 issued to Dutton discusses in some detail the problem in detecting the pump-off condition and providing adequate means to minimize the problem. Dutton proposes a flow meter arrangement for determining the volume of fluid being pumped and the pumping is shut down when measurement from the flow meter indicates a decline in pump efficiency, which indicates that the production fluid level in the tubing has fallen below the upper most travel of the plunger.
Another attempt to provide a pump-off control device utilizes the measurement of the length of time required for the pump to down stroke with a full barrel of oil and the time interval for the down stroke with less than a full barrel of oil. By these two measurements, pump-off is determined and the well shut down to prevent excessive fluid pound. The pump is allowed to pump a pre-determined number of cycles and if fluid pound is reached again, the time is reset on the new information.
Another system for pump-off control utilizes wave-form signals proportional to the load on the motor drawing the pump to determine the change in load wave-form when the pump is at pump-off.
The present invention provides a pump-off control system for sucker rod or beam pumping units, in which the pump motor is shut-off when the sucker rod unit undergoes fluid pound, which jolts the sucker rods. This action interrupts the electrical circuit supplying power to the pump motor. To accomplish this, Applicant mounts the pump-off interrupter on top of the polished rod on the balance beam pumping unit. The interrupter has a fixed electrical contact that moves with the movement of the polished rod and a floating electrical contact that rests on the fixed contact. When fluid pound occurs, there is sufficient jolt to the polished rod to cause the fixed and floating contacts of the interrupter to part, thus interrupting an electric circuit, which holds a normally open contact of a time delay relay closed as long as voltage is applied across the relay. In this fashion, when the relay opens by interruption of the electric circuit, power to the motor is interrupted until the electrical circuit is completed through the time delay relay. The time delay may be set to retain the well shut in for a sufficient amount of time to permit the fluid in the well bore of the reservoir to rise above the plunger to again efficiently pump oil from the reservoir.
It is therefore an object of the invention to provide a circuit interrupter attached to the polished rod, which opens a relay when the polished rod undergoes fluid pound shutting down the sucker rod pump.
It is another object of the invention to provide a pump-off interrupter mounted on the polished rod, which includes an insulated cylinder with one end attached to a metallic cylinder filled with Babbitt metal with a metallic disc attached to the Babbitt metal to provide one side of an electrical contact. The metallic cylinder is secured to the polished rod. A second metallic cylinder, with Babbitt metal to provide sufficient weight, secures a metallic disc to form the other side of an electrical contact, such that the contact is maintained during normal pumping operation of the balance beam pump and upon incurring fluid pound, the two contacts will separate from the impact shutting down the pump.
It is an additional object of the invention to provide a pump-off control mounted on the polished rod, which includes a plastic cylinder with one end securely attached by metallic material to the polished rod to provide one side of an electrical contact within the plastic cylinder. A metallic cylinder with metallic material secured in one end to form the other side of an electrical contact, including a series of removeable metal disc to provide sufficient weight to maintain the contact closed during normal operation and responding to fluid pound to break the electrical connection.